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Bacteria and Viruses

Genetically altered bacteria and viruses are also used in agriculture. Originally, genetic engineering techniques worked well only with animal cells, because plants have tough cell walls that most bacteria can not get through. And those that can are usually harmful. But scientists found a way to take a harmful bacterium called Agrobacterium tumifaciens, which normally causes crown gall disease, and make it beneficial. The bacterium infects a plant by inserting its DNA into the plant cell, which...

The surface of germs such as bacteria carry markers called antigens, which enable lymphocytes to identify invading germs. Each lymphocyte recognizes a specific antigen, just as a key fits a lock. The surface of germs such as bacteria carry markers called antigens, which enable lymphocytes to identify invading germs. Each lymphocyte recognizes a specific antigen, just as a key fits a lock. Antibody locks onto bacterium, marking it for destruction When the lymphocyte recognizes bacteria by their...

Where could these horrific diseases come from They mysteriously came upon a person, gripping him or her with terrible symptoms and then quickly spread through a community. Ethnic and religious groups were often blamed for the disease. English nurses tend to smallpox patients in this nineteenth-century illustration. Although a vaccine exists today, deadly outbreaks of smallpox have been common throughout history. Prior to the 1800s most people believed that epidemics like the plague and smallpox...

Although Pasteur created a vaccine for rabies, he never saw the organism that caused this dreaded disease. Many other scientists who worked on plant and animal infections assumed they were looking for bacteria, but they would never find them. What they did find was something smaller and more puzzling. In 1886 Adolf Mayer, a German scientist, was researching the tobacco mosaic disease, so called because it left the leaves of the tobacco plant shriveled and mottled. Mayer believed that the...

Other microbes are hard at work cleaning oil spills. In March 1989, when the Exxon Valdez oil tanker spilled Workers clean rocks after the 1989 Exxon Valdez oil spill. During the cleanup, researchers learned that naturally occurring bacteria convert oil into a completely harmless substance. more than 11 million gallons of crude oil, it contaminated hundreds of miles of shoreline. Cleanup crews worked furiously to save the wildlife, but in the end, more than a quarter of a million birds, five...

A person is injected with a harmless form of the germ, which does not cause the disease. Although the germ is harmless, the body still recognizes it and makes antibodies against it. If the body is invaded by the disease-causing form of the germ, the immune system responds immediately with huge numbers of antibodies to destroy the germ. This type of immunization uses a form of the disease-causing germ that has been slightly altered to stop it from causing the disease. The person receiving it...